1. Field of the Invention
The present invention is directed to an apparatus for determining a coordinate transformation for mixing an image of a first subject into an X-ray image of a second subject.
2. Description of the Prior Art
Navigation is being increasingly practiced for supporting medical interventions at living subjects, this being defined as the guidance of a medical instrument relative to a living subject or relative to a tissue region of the living subject being treated, that is supported with optical image information. An image of the instrument is thereby mixed into an image of the living subject acquired with an X-ray apparatus, such as a 2D or 3D image. In this way, an operator can guide an instrument that has at least partly penetrated into the living subject, the tip of which is no longer directly visible because it has penetrated into body tissue. This guidance ensues relative to the tissue region of the living subject to be treated on the basis of the image information without a risk of unintentional harm to the life form.
In order to enable such a navigation-guided intervention, i.e. in order to be able to mix an image of the instrument into image information of a living subject with exact position and attitude, it is necessary to produce a mathematical relationship in the form of a coordinate transformation between the coordinate system of the image information of the living subject, or a coordinate system of the reconstructed volume of the subject and a coordinate system with respect to which the positions of the instrument to be navigated are defined. Heretofore, artificial marks or anatomical marks, for example pronounced bone structures, have sometimes been defined at the subject. The anatomical or artificial marks must be clearly visible in the image information of the subject registered with the X-ray apparatus and must be easily accessible at the subject. The artificial marks, for example, are secured to the skin surface of the life form in order to be able to undertake a procedure referred to as a registration, which is understood as the determination of the spatial transformation rule between the coordinate system in which the positions of the instrument to be navigated are indicated and the image information or of the subject the reconstructed volume thereof, employed for the navigation. The marks usually must be individually approached with the instrument in order to be able to determine the coordinate transformation between the two coordinate systems. The registration of the marks is therefore a relatively time-consuming process for an operator.
German OS 199 09 816, for example, discloses a navigation system for the implementation and support of surgical interventions, wherein the system has access to an image data bank for pre-operatively prepared nuclear magnetic resonance and/or computer tomography data. Marks that are visible in the images of the patient are arranged at the patient. Ultimately, a transformation relationship between the images made of the patient and the coordinate system allocated to the navigation system can be produced in a registration procedure wherein the marks arranged at the patient are approached with an instrument, the positions of which can be determined with a navigation system.
German OS 199 17 867 discloses an apparatus for determining a coordinate transformation that includes means (which are not specified in detail) for fastening the apparatus to a subject, which can be a patient. The apparatus has an adapter with markers that can be acquired by a navigation system and also has a reference structure with X-ray-positive marks. A coordinate transformation between a coordinate system allocated to a navigation system and a coordinate system allocated to an X-ray image can be produced on the basis of the reference structure and the adapter.
German OS 195 15 748 discloses a therapy apparatus for treating a body region of a patient with acoustic waves, wherein the spatial allocation of the patient and a source of acoustic waves of the therapy apparatus (required for the treatment) relative to one another is accomplished by means of a workstation and with the use of 3D navigation systems on the basis of images of the body region of the patient to be treated that are acquired with an imaging device independently of the therapy apparatus, and that are displayed on a picture screen of the workstation.
German OS 199 51 502 also discloses a system that has an image pick-up device for acquiring images of a patient and a navigation system for determining the position of the image pick-up device as well as for determining the position of a subject to be moved relative to the patient. By determining the position of the instrument relative to the image pick-up device, an image of the medical instrument can be mixed into an image of the patient acquired with the image pick-up device.